1. Field of the Invention
The present invention relates generally to an over-the-desk document scanning system, and more particularly to, a method and apparatus for generating a composite image of a hardcopy document using images from multiple video cameras.
2. Description of Related Art
Over-the-desk scanning systems that position a video camera above a desk to capture images of hardcopy document are known. An example of such an over-the-desk scanning system is disclosed by Wellner in U.S. Pat. No. 5,511,148 entitled xe2x80x9cInteractive Copying System.xe2x80x9d In operation, the over-the-desk scanning system captures images of hardcopy documents and digitizes them for further processing. These captured images of hardcopy documents arranged on a desk are subsequently displayed on a computer monitor immediately coupled to the over-the-desk scanning system or remotely coupled via a network that form part of a video conferencing system.
Over-the-desk (i.e., face-up) scanning of hardcopy documents with a video camera has several advantages over traditional face-down scanning techniques. One advantage of face-up scanning is that a hardcopy document can be simultaneously read on a physical desktop and scanned without requiring the hardcopy document to be repositioned in a face down orientation. This advantage provides seamless integration between working hardcopy documents positioned on a physical desktop and the electronic document applications operating on a computer to which the over-the-desk video camera is coupled. Another advantage is that additional elements, such as a pointing finger, can be captured, for example, to annotate the hardcopy document in its corresponding scanned representation during a video conferencing session.
Although the use of video cameras is very effective with video conferencing applications, video cameras do not typically yield images with sufficient quality (i.e., resolution) to enable successful document decoding using OCR (Optical Character Recognition). Never the less, it would be desirable for an over-the-desk document scanning system to record large high resolution images of hardcopy documents. These recorded large high resolution images could then either be broadcast as part of a video conferencing system or be edited for use with or in other electronic documents. Furthermore, in order for such an interactive over-the-desk scanning system to perform effectively, it would be desirable that such a system be adapted to record images of hardcopy documents that have an undetermined thickness. It would therefore be advantageous to provide an over-the-desk document scanning system that is adapted to both efficiently generate large high resolution images using video cameras in a manner that is independent of the thickness of a hardcopy document.
In accordance the invention, there is provided an apparatus and method therefor, for scanning hardcopy documents. The apparatus includes an image acquisition system and a frame merger module. Initially, the image acquisition system simultaneously records parts of a hardcopy document positioned face-up on a work surface. The parts of the hardcopy document are recorded without perspective distortion in a first image and a second image by the image acquisition system. A portion of each of the parts of the hardcopy document recorded in the first image and the second image record an identical segment of the hardcopy document. Subsequently, the frame merger module forms a composite image of the hardcopy document by stitching the first image and the second image together at the portions in each image that record the identical segment of the hardcopy document. The frame merger module identifies the portion in the first image and the portion in the second image by computing correlation values of high gradient images of the first image and the second image for different regions of overlap between the first image and the second image.